1. Field of the Invention
This invention relates to the electric lamp art and has particular reference to an improved integral fuse structure for a gas-filled incandescent lamp.
2. Description of the Prior Art
Incandescent electric lamps that contain an inert fill gas and are provided with an integral fuse component are generally well known in the art. A double-ended halogen-cycle incandescent lamp which contains a coiled-coil filament that is terminated by an uncoiled leg section which functions as a fuse and is fastened to the end of a lead-in conductor that is embedded in the envelope seal is disclosed in U.S. Pat. Nos. 3,211,942 (E. H. Wiley) and 3,211,950 (J. G. Cardwell, Jr.), both issued Oct. 12, 1965. A modified lamp of this type in which the combined functions of a fuse and a filament support are achieved by a wire member that is fastened to the embedded end of the lead-in conductor and has its opposite end wound around the singly-coiled leg segment of a coiled-coil filament to provide an interwound juncture is disclosed in U.S. Pat. No. 3,211,943, which was also issued to J. G. Cardwell, Jr. on Oct. 12, 1965.
A fuse assembly that constitutes an integral part of a double-ended incandescent lamp but is disposed within a ceramic cap attached to the press seal and is thus located outside of the lamp envelope is disclosed in U.S. Pat. No. 3,274,426, issued Sept. 20, 1966 to R. F. Scoledge et al. An improved exterior fuse assembly for such a lamp in which a separate support wire for the lamp contact is employed and connected to a protruding portion of the lead-in conductor by the fuse wire is shown in U.S. Pat. No. 3,346,768, issued Oct. 10, 1967 to G. F. Patsch.
Halogen-cycle type incandescent lamps having fuse elements in the form of rods or metal foils that are completely embedded in the press seals and connected to the ends of the coiled filament are disclosed in U.S. Pat. No. 3,710,169 (G. R. T'Jampens et al.), issued Jan. 9, 1973 and Japanese Patent Publication No. 47-11421 of Ito et al., published Apr. 27, 1972. A double-ended incandescent lamp having an internal fuse element in the form of a wire that is coiled around a separate spud wire which is connected to one end of the filament and is embedded in the press seal is disclosed in U.S. Pat. No. 3,864,598, issued Feb. 4, 1975 to J. G. Cardwell, Jr. The uncoiled end of the fuse wire is connected to a foil conductor embedded in the seal, thus completing the electric circuit. A single-ended halogen-cycle incandescent lamp having an internal fuse in the form of a coiled wire that is connected to the inwardly-extending ends of an internal lead wire and an external lead-in conductor assembly that are both embedded in the hermetic seal and both protrude into the envelope is disclosed in Japanese Patent Publication No. 48-30707 of Toyoda, published Sept. 19, 1973. A single-ended halogen-cycle projection type incandescent lamp with an internal platinized fuse wire is disclosed in U.S. Pat. No. 3,727,091 issued Apr. 10, 1973 to A. R. DeCaro.
While the prior art structures which employed external fuse components were generally satisfactory from a functional standpoint, they were rather complicated and expensive in that they required several accurately-formed parts to hold and protectively enclose the fuse assembly. Even though the expense of such additional parts was eliminated by using internal fuse components, the prior art practice of using a coiled fuse wire or coiling one end of an internal fuse wire around the filament leg or a spud wire made it difficult and expensive to manufacture the lamp since highly-skilled manual labor was required to make such assemblies. In addition, the resulting electrical juncture of the parts was not very rugged or reliable and left much to be desired from the standpoint of a positive and durable electrical connection. This is a particularly vexing problem in prior art halogen lamps that employ tungsten inner lead wires and tungsten wire fuses that are welded to each other (as in the aforementioned pending application Ser. No. 731,393, now U.S. Pat. No. 4,066,926, of R. E. Newton) insofar as such tungsten-to-tungsten welds are very difficult to control and make in the factory on a mass-production basis. This is due to the fact that the tungsten tends to crystallize and become brittle when heated during the welding operation.
In some cases, the spacing between the internal metal components of the lamp was so close that an electric arc could easily "bridge" the gap between them after the fuse element melted, thus preventing reliable arc-suppression as the lamp failed and creating a potential safety hazard.